This disclosure relates to the design of a lower noise gas turbine engine turbine.
Gas turbine engines are known, and typically include a fan delivering air into a compressor. The air is compressed in the compressor and delivered downstream into a combustor section where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors, driving the turbine rotors to rotate.
Typically, there is a high pressure turbine rotor, and a low pressure turbine rotor. Each of the turbine rotors include a number of rows of turbine blades that rotate with the rotor. Interspersed between the rows of turbine blades are vanes.
The high pressure turbine rotor has typically driven a high pressure compressor rotor, and the low pressure turbine rotor has typically driven a low pressure compressor rotor. Each of the compressor rotors also include a number of compressor blades that rotate with the rotors. There are also vanes interspersed between the rows of compressor blades.
The low pressure turbine or compressor can be a significant noise source, as noise is produced by fluid dynamic interaction between the blade rows and the vane rows. These interactions produce tones at a blade passage frequency of each of the low pressure turbine rotors, the low pressure compressor rotors, and their harmonics.
Historically, the low pressure turbine has driven both a low pressure compressor section and a fan section. More recently, a gear reduction has been provided such that the fan and low pressure compressor can be driven at distinct speeds.
With the inclusion of a gear, low pressure turbine speeds have increased. Thus, to “cutoff” these turbines, vane-to-blade ratios must be higher than for turbines in a conventional engine.